The term “biomass” generally refers to the total amount of organisms that inhabit or exist in a given area. When such term is used with regard to plants, in particular, it refers to dry weight per unit area. Biomass units are quantified in terms of mass or energy. The expression “biomass” is synonymous with “Seibutsutairyo” or “Seibutsuryo.” In the case of plant biomass, the term “standing crop” is occasionally used for “biomass.” Since plant biomass is generated by fixing atmospheric carbon dioxide with the use of solar energy, it can be regarded as so-called “carbon-neutral energy.” Accordingly, an increase of plant biomass is effective for global environmental preservation, the prevention of global warming, and mitigation of greenhouse gas emissions. Thus, technologies for increasing the production of plant biomass have been industrially significant.
Plants are cultivated for the purpose of using some tissues thereof (e.g., seeds, roots, leaves, or stems) or for the purpose of producing various materials, such as fats and oils. Examples of fats and oils produced from plants that have been heretofore known include soybean oil, sesame oil, olive oil, coconut oil, rice oil, cottonseed oil, sunflower oil, corn oil, safflower oil, palm oil, and rapeseed oil. Such fats and oils are extensively used for household and industrial applications. Also, fats and oils produced from plants are used as raw materials for biodiesel fuel or bioplastic, and the applicability thereof is increasing for alternative energy to petroleum.
In particular, an energy crop such as sugar cane can be used as a raw material for biofuel. Hence, the increased production of the total mass of a plant itself (the amount of plant biomass) is expected. Under such circumstances, improvement in productivity per unit of cultivation area is required in order to increase the production of the amount of plant biomass. It has been found that if the number of cultivated plants is assumed to be constant per unit of cultivation area, improvement in the amount of biomass per plant would be necessary.
However, it is thought that since many genes are involved in the amount of plant biomass (a so-called “kind of quantitative trait”), individual gene introduction or individual genetic modification cannot lead to an effective increase in the production of plant biomass. Meanwhile, a great deal of difficulties are associated with introduction of many genes in a desired state into a plant. Such gene introduction is also problematic in that if successful gene introduction takes place, desirable traits cannot always be acquired.
Various gene transfer techniques are known as techniques for increasing the production of plant biomass, as disclosed in JP Patent Publication (Kohyo) No. 2001-505410 A; JP Patent Publication (Kohyo) No. 2001-519659 A; JP Patent Publication (Kohyo) No. 2007-530063 A; JP Patent Publication (Kokai) No. 2005-130770 A; JP Patent Publication (Kohyo) No. 2000-515020 A; JP Patent Publication (Kohyo) No. 9-503389 A (1997); and JP Patent Publication (Kokai) No. 2005-52114 A, for example. However, according to techniques disclosed in Patent Documents (JP Patent Publication (Kohyo) No. 2001-505410 A; JP Patent Publication (Kohyo) No. 2001-519659 A; JP Patent Publication (Kohyo) No. 2007-530063 A; JP Patent Publication (Kokai) No. 2005-130770 A; and JP Patent Publication (Kohyo) No. 2000-515020 A), only the effects of increasing the production of partial plant biomass, such as plant seeds, tubers, roots, and leaves, can be obtained. Also, techniques disclosed in JP Patent Publication (Kohyo) No. 9-503389 A (1997) and JP Patent Publication (Kokai) No. 2005-52114 A disclose only the effects of increasing the production of biomass under nitrate-unlimited growth conditions or by delaying the flowering time so as to lengthen the growth period. Hence, Patent Documents (JP Patent Publication (Kohyo) No. 2001-505410 A; JP Patent Publication (Kohyo) No. 2001-519659 A; JP Patent Publication (Kohyo) No. 2007-530063 A; JP Patent Publication (Kokai) No. 2005-130770 A; JP Patent Publication (Kohyo) No. 2000-515020 A; JP Patent Publication (Kohyo) No. 9-503389 A (1997); and JP Patent Publication (Kokai) No. 2005-52114 A) disclose no techniques for achieving the effects of increasing the production of the biomass of an entire plant through application of general culture and/or growth conditions.